All viruses must bind to and invade their target cells to replicate. For enveloped animal viruses, including RNA viruses having Class I membrane fusion proteins (Type I viruses), the process involves (a) binding of the virion to the target cell, (b) fusion of the envelope of the virus with the plasma membrane or an internal cellular membrane, (c) destabilization of the viral envelope and cellular membrane at the fused area to create a fusion pore, (d) transfer of the viral RNA through the pore, and (e) modification of cellular function by the viral RNA.
Fusion of the viral membrane and the cell envelope, steps (b) and (c) above, is mediated by the interaction of a viral transmembrane glycoprotein (fusion protein) with surface proteins and membranes of the target cell. These interactions cause conformational changes in the fusion protein that result in the insertion of a viral fusion peptide into the target cell membrane. This insertion is followed by further conformational changes within the fusion protein that bring the viral envelope and cell membranes into close proximity and results in the fusion of the two membrane bilayers.
Identification of classes of RNA Type I viruses and fusion proteins and methods of inhibiting the function of the fusion initiation region in RNA viruses are described in PCT/US2004/036578, filed Nov. 3, 2004, and U.S. application Ser. No. 12/452,240, filed Dec. 22, 2009, each of which is incorporated herein by reference in its entirety.
The Arenaviridae family of enveloped, negative-stranded RNA viruses encompasses a number of hemorrhagic fever (HF) viruses, five of which have been designated category A agents by the CDC and NIAID. Lassa virus (LASV) is the most prevalent of the HF viruses, with approximately 500,000 cases estimated annually in West Africa. Outbreaks of arenavirus HF occur sporadically in South America, as well, and mortality rates in hospitalized cases can exceed 40%. Clinical treatment of arenavirus infection is currently limited to administration of the nucleoside analogue ribavirin, which is marked by significant toxicity and sub-optimal efficacy.
Arenavirus infection is initiated by its glycoprotein complex (GPC), which is expressed as a polypeptide and cleaved into three segments by a signal peptidase and SKI-1/S1P. The mature glycoprotein spike consists of a receptor-binding subunit (GP1), a membrane-anchored fusion protein (GP2), and a unique signal peptide. At 58 amino acids in length, the arenavirus signal peptide is 2-4 times longer than most viral signal peptides. It features two transmembrane domains and remains associated with GP2, with a possible role in spike stability.
The Arenavirus GP2 is considered a class I viral fusion protein on the basis of its α-helical major domains. Following receptor binding and endocytosis, the decreased pH disrupts GPC intermolecular and intramolecular bonds. Dissociation of GP1 exposes the fusion peptide region of GP2, which can insert into the endosomal membrane. Virus-cell fusion is mediated by the rearrangement of GP2 trimers into a lower-energy conformation, the six-helical bundle (6-HB), bringing together the viral and endosomal bilayers. The entry process represents a potential target for antiviral agents, one of the most notable entry inhibitors being the HIV drug enfuvirtide. Derived from the C-terminal heptad repeat (CHR) of HIV gp41, enfuvirtide is a peptide inhibitor of viral fusion and prevents stable 6-HB formation. Fusion inhibitors of similar design have been reported for coronaviruses, flaviviruses, orthomyxoviruses, paramyxoviruses, and filoviruses. Peptide drugs generally possess high specificity and low toxicity.
There is an ongoing need for peptide drugs and methods for treating arenavirus infections. The peptide, compositions, and methods described herein address this need.